1. Field of the Invention
The present invention relates to a cooling tower used in air conditioning or cooling facilities utilized in buildings, factories and so forth, and to a lower water tank included therein, and further to a method of manufacturing a semiconductor device.
2. Description of the Background Art
Referring to FIG. 5, a positioning of a cooling tower is described. A cooling tower 10 is fed with heated circulating water (also referred to as xe2x80x9ccooling waterxe2x80x9d) from a refrigeration machine 12 in an air conditioning or cooling facility, releases heat of the circulating water by exchanging the heat between the circulating water and outside air, and subsequently feeds the circulating water back to the refrigeration machine. Cooling tower 10 has a water tank 11 as a so-called lower water tank. Water tank 11 receives and impounds the circulating water sprinkled within cooling tower 10.
In water tank 11 with a suction opening 5 on a bottom surface 6 as shown in FIG. 6, the circulating water can be circulated without a problem when a water level is high enough, while a vortex 3 tends to be generated above suction opening 5 as a water level 4 attains to a certain level or lower. If this vortex 3 develops, the water surface may go down toward the center of the vortex and air may be sucked in from suction opening 5. This tends to occur particularly at a startup. Air suction from suction opening 5 is problematic, as heat-exchange effectiveness in refrigerator 12 may be reduced, or the refrigerator may even be stopped in an extreme case.
In order to avoid this problem, a conventional technology has been proposed in that a water depth of water tank 11 is made deeper. However, increasing of the water depth of water tank 11 increases weight of cooling tower 10, which will be inconvenient since, when water tank 11 is located on a structure such as a building, an engineering work may be required to reinforce the structure.
Further, a method of controlling a pumping ability of a pump at a startup, and a method of providing a mechanism preventing air from flowing in by a mechanical operation as disclosed in Japanese Patent Laying-Open No. 11-304397, have been proposed. However, a control mechanism such as a water level sensor must be provided to control a pumping ability of a pump at the startup, resulting in a complicated structure of the cooling tower and increased cost. Even when the mechanical operation is employed, a structure performing the mechanical operation must be incorporated, also resulting in increased cost. Further, as long as it is an operating machine, a possibility of failure could not be eliminated.
An object of the present invention is, therefore, to provide a water tank having a simple structure and capable of preventing suction of air without any increase of weight and cost, a cooling tower including the water tank, and a method of manufacturing a semiconductor device.
To accomplish the object described above, a water tank according to the present invention includes a bottom surface having a suction opening for draining water, and an air-suction preventing member covering the suction opening, spaced with a gap allowing water to flow into the suction opening, above the bottom surface. As the suction opening is covered by the air-suction preventing member, this arrangement can prevent a vortex from generating around the center of the suction opening even when a water level is lowered, and hence can prevent air from being sucked in.
In the invention described above, preferably, the air-suction preventing member is so arranged as to interrupt the suction of air by the suction opening due to the generation of the vortex at the suction opening. This arrangement allows an air-sucking phenomenon caused by the generation of the vortex to be interrupted by the air-suction preventing member. Thus, the air suction can be prevented.
A cooling tower according to the present invention includes the water tank described above. This arrangement can prevent air suction by a suction opening even when a water level of the water tank is lowered, and therefore, the cooling tower is free from the problem such that heat-exchange effectiveness of a refrigerator is reduced, or the refrigerator is stopped.
A method of manufacturing a semiconductor device according to the present invention uses the cooling tower described above. The method allows stable cooling and hence stable manufacturing of a high-quality semiconductor device.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.